Cephalosporin analogs having an oxygen atom in place of the sulfur atom in the nucleus have been described in the Journal of Heterocyclic Chemistry, Volume 5, page 779 (1968) by J. C. Sheehan and M. Dadic; German Patent Application (OLS) No. 2,219,601 (1972); Canadian Journal of Chemistry, Volume 52, page 3996 (1974) by S. Wolfe et al.; the Journal of the American Chemical Society, Volume 96, page 7582 (1974) by B. G. Christensen et al.; and Japanese Patent Application (unexamined publication) no. 49-133,594 claiming priorities based on U.S. Patent Application Nos. 303,905 and 395,662.
However, the above references did not disclose the Compounds I specifically. Now, the present inventors have found the superior antibacterial activity of specific Compounds I and this discovery has led to this invention.